A fuel cell stack is formed by stacking a plurality of single cells between two end plates and applying a fastening load in the stacking direction by means of fastening bolts and/or a casing. Each of the single cells includes a pair of separators that include corrugated plates and a fuel cell electrode structure which is a membrane electrode assembly integrally formed with a frame and is held between the pair of separators.
The membrane electrode assembly includes an electrolyte membrane and a pair of electrodes disposed on both faces of the electrolyte membrane. Each of the electrodes includes a catalyst layer and a gas diffusion layer formed on the outer face of the catalyst layer. For example, carbon paper or the like with water repellant finish is used as the gas diffusion layer.
Gas channels are formed between the membrane electrode assembly and the corrugated plates along a reaction surface. In order to prevent fuel gas or oxidant gas that are supplied to the gas channels from leaking to the outside or to prevent the fuel gas from being mixed with the oxidant gas, a scaling member is provided on the periphery of the membrane electrode assembly.
Patent Document 1 discloses a membrane electrode structure that is joined on the outer periphery of electrodes, with gaskets that are punched into the approximately same shapes as outer peripheral parts of separators and are put on both side of an electrolyte membrane. In the membrane electrode structure, faces of the separator in contact with the electrodes are at a level higher than the faces on the periphery in contact with the gasket. The Document 1 also discloses that even when this results that a thin electrode membrane structure is employed, the gasket can be adequately compressed, and thereby gas in the fuel cell does not leak to the outside of the fuel cell.
Patent Document 2 discloses that liquid sealer is applied to grooves formed in the rims of separators, a pair of the separators holds an electrode membrane structure to squeeze the liquid sealer, and the liquid sealer is closely contacted with the end faces of gas diffusion layers of the electrode membrane structure to prevent reaction gas from flowing through the periphery of the electrode membrane structure.